DE1210416B - Process for separating metal ions - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY GERMAN ^ tMS PATENTAMT Int. Cl .:

BOId

EDITORIAL

Number:
File number:
Registration date:
Display day:

German class: 12 d- 1/03

1210416
S 62437IV a / 12 d
April 3, 1959
February 10, 1966

The present invention relates to a method for the selective separation or enrichment of Cations from acidic aqueous solutions containing cations, in particular for the separation of metal ions.

The method of the invention is particularly suitable for separating monovalent cations with relatively large crystallographic radii that oppose oxidation to a polyvalent state stable or relatively stable, from each other and / or from other ions.

The method is also applicable to the fractionation of ion mixtures into fractions monovalent, divalent and trivalent metal ions.

The invention is general in various fields insofar as it relates to separation or concentration of ions are applicable. The most important area of application, however, is treatment radioactive waste products from nuclear reactors. The invention should therefore with particular reference ao this area of application will be described in detail.

It is relatively difficult to separate alkali compounds from one another. This is especially true for the Connections of rubidium and cesium. These connections are relatively rare, and it is difficult to keep them pure.

In addition, it is difficult to concentrate these ions when they are in relatively low concentrations are present.

Closely related to this problem is the problem of separating some of the radioactive components from the fission products of uranium in the waste products of nuclear reactors. One of these fission products is Cs ¹³⁷ .

The development of a simple method for the pure preparation of Cs ¹³⁷ would increase the usability of this substance as a technical radiation source.

The development of a process by which Cs ¹³⁷ can be produced with practically no inactive impurities would therefore represent a great step forward.

The solutions that arise as waste products from nuclear reactions mainly contain the residues those after the dissolution of the nuclear energy sources in strong nitric acid etc. and separation of uranium and plutonium are left behind by solvent extraction. These solutions contain hence nitric acid in high concentration.

Organic ion exchange resins are extremely good at achieving separation of some metal ions Process for separating metal ions

Applicant:

South African Council for Scientific

and Industrial Research, Pretoria,

Transvaal (South Africa)

Representative:

Dr. F. Zumstein,

Dipl.-Chem. Dr. rer. nat. E. Assmann

and Dipl.-Chem. Dr. R. Koenigsberger,

Patent Attorneys, Munich 2, Bräuhausstr. 4th

Named as inventor:
Jakob van Rouendal Smit,
Pretoria, Transvaal (South Africa)

Claimed priority:

South Africa of April 3, 1958 (1157),

Great Britain January 26, 1959 (2787) -

usable. However, when used for radioactive materials, they are subject to radiation damage. In addition, the selectivity of such ion exchangers when applied to waste products nuclear reactions often leave a lot to be desired. This also applies to the well-known inorganic ones Ion exchangers, which also usually have a low capacity. Organic exchangers are used Treatment of strongly acidic solutions unsuitable.

The present invention aims to provide an efficient method for separating or concentrating Cations from fission products and other solutions using ion exchangers with high Capacity.

Such an ion exchanger for the purposes mentioned above must not be noticeably attacked by radiation and must normally be placed on an industrially usable ion exchanger Requirements are sufficient, d. H. not just on and near its surface, but throughout the material ensure a quick exchange, d. that is, it must be sufficiently porous to allow a sufficient percolation rate to allow; Furthermore, it must have a high capacity and selectivity for certain cations, and the reversibility of the ion exchange must be guaranteed.

The method of the present invention for the selective separation or enrichment of ca-

609 507/234

3 4

Cations from acidic aqueous cations are found to have a great diversity of distribution solutions by means of a fixed inorganic coefficient Ka of the individual cations.
Cation exchanger and optionally washing out The selectivity for Cs of these ion exchangers is carried out by the exchanger, and the innovation, which is extraordinarily high according to the invention under strongly acidic conditions, consists in the fact that the exchange of ammonium phosphomolybdate, ammonium, and ammo- normally not exchanged, in the iüumphosphotungstat, ammonium arsenomolybdate solution is not very much reduced. So is the or ammonium arsenotungstate, if necessary, on the partition coefficient
a carrier, is used and that the pH

the solution to be treated or the aqueous io. Quantity X

Washing liquid to enable selectivity _{Kd =} per gram of exchanger ^ _equilibrium)

of exchange depending on the ions to be exchanged, amount X per milliliter of solution
is set.

The acidic conditions under which the ver, where X is the ion species in question, of Cs

driving takes place, preventing the decomposition of the 15 with ammonium phosphomolybdate in n / 10-NH ₄ NO ₃

Ion exchanger. about 6000, while the corresponding value for Cs

By adjusting the pH of the aqueous in undiluted seawater from pH 3.6 to about 1500

The solution is in your hand, the exchange amounts. This enables direct selective adsorption

to enable or prevent certain cations. of Cs from concentrated acidic solutions

So from an acidic medium with a pH of 20 a salt or salt mixture with exception

Value below about 1 only monovalent cations with those of K ⁺ , NH ₄ ⁺ , Rb ⁺ , Tl ⁺ , Ag ⁺ and Hg ⁺

relatively large ionic radius, which enables resistance to. That is a salient quality

an oxidation into a polyvalent state, of the exchangers used according to the invention. It

exchanged. Examples of monovalent ions, which below can be shown to be the value of Ka of the ammo

These conditions can be extracted are 25 nium ion concentration is inversely proportional.

K ⁺ , Rb ⁺ , Cs ⁺ , Tl ⁺ and Ag ⁺ . Na ⁺ becomes from some At NH ₄ + -concentrations below n / 10 is the JTa-value

Solutions extracted to a small extent, but for Cs even higher than indicated above,

not if other ions competing with it, such as the only ones besides Cs under these conditions

for example ammonium ions in noticeable con-exchangeable ions, which are formed in nuclear reactions

centrations are present, and Li ⁺ can become 30 at all and therefore present in fission product solutions

cannot be extracted. Therefore it is possible to be selective, Rb ⁺ and Ag ⁺ , are only in extraordinary

radioactive cesium from a strongly acidic solution is present in low concentrations and affects

separated from fission products, so that a larger influences the Ka value of Cs ⁺ only negligible.

Impurities in this cesium only include the chemicals used during processing

listed monovalent cations, insofar as they are in the 35 kalien etc. can also contain small amounts of NH ₄ ⁺

original solution are present, in question and K ^{+ be} present.

come. As explained in more detail later, it is also the interaction between ion exchangers possible to these ions, regardless of whether they and. aqueous phase can according to the invention for the purpose are radioactive or not by the process of achieving cation enrichment in an invention from each other too. separate. 40 always wanted direction to one or

The adjustment of the pH value, in particular with both of the following possibilities:

Working in the moderately acidic pH range, take A. The total amount of all in one to be treated

preferably with a buffer substance. Dissolution of existing exchangeable cations

To enable the exchange of bivalent and / or exceed the capacity of the exchanger or trivalent cations, especially cations 45 under the exchange conditions. As a result of elements of the II. And III. Group of the peri-, an enrichment of those cations in the odic system including the rare earth ion exchangers takes place, for which the ion metals and yttrium, from one of the exchangers, has the highest selectivity,
solution containing monovalent cations B. A previously "charged" with cations exchanging moderately to weakly acidic conditions is kept in contact with another aqueous solution, in particular a pH value of the solution is brought into contact, whereby a solution of 2 or above, preferably over 2.7. new distribution relationship arises and the on

The weakest is preferably bound to the ion exchanger as the ion exchange substance

readily available ammonium phosphomolybdate (APM) cations preferentially into the aqueous solution

used. 55 hike.

It has been known for some time that ammo is the value of the process of the invention

Niumphosphomolybdate certain ion exchanges - not only in that the ions selectively from one

owns. However, nothing was known about the fact that the solution could be removed (in order to then

that and in what way these properties are recovered for better, possibly known ways

complicated separations can be exploited. To be 60), but also precisely in the fact that the extra-

Rather, some of the ions valued in the literature had to be gradually removed from the ion exchanger

Ammonium phosphomolybdate ascribed to its own can be separated off, so that a separation

shafts (slow exchange reaction with alkali these ions from each other can be achieved.

metal ions in neutral aqueous solution) this for preferably these ions are fractionated by the a practical ion exchange is unsuitable. 65 ion exchangers are eluted, for example by

let shine. as eluent solutions of ammonium salts

The selectivity to be used according to the invention is used in a suitable concentration. A suitable one

The ion exchange substances are based on the now eluant is ammonium chloride in aqueous

Solution, the concentration of which can be increased from time to time during the elution. Desired- or, if necessary, the eluent can be a hydrogen halide, for example hydrogen chloride, be added in a suitable concentration. Another suitable eluant is ammonium nitrate in aqueous solution with or without the addition of nitric acid.

The above-mentioned chromatographic separation may also be suitable for further separation Purification of a cation material which has already been enriched in a previous process stage. For example, one can be obtained by any of the methods described above Add cesium concentrate for further cleaning chromatograph in the manner just described.

To put the different types of ions in the order to elute increasing absorbability, one gradually increases the concentration of the ammonium and / or hydrogen ions in the eluting solution.

The method according to the invention finds a useful application in the production of gamma-active solutions, where from time to time the barium formed by radioactive decay is removed from an ion exchanger of the type mentioned, preferably an ion exchanger with ammonium phosphomolybdate as the ion-exchanging component, which is loaded ^{with radioactive cesium, in particular Cs 137} 137 eluted. In the laboratory, a so-called gamma milk is used for this purpose, which essentially consists of a column filled with the ion exchanger. The ion exchange column loaded with cesium 137 and a container for the eluting solution can be accommodated in a manner known per se as a unit in a cartridge.

One when working with the ammonium salts mentioned above to be used according to the invention The problem that often arises with heteropoly acids is that these substances are normally present in very large quantities fine distribution can be obtained. In this form, however, these substances are suitable for use in unsuitable for large columns. Preferably, therefore, is that used for the method of the invention Ion exchangers in coarse, z. B. granulated or pelletized form with or without a binder, such as silica gel, applied.

The * ion exchanger of the invention can also consist of one of the ammonium salts described Heteropolyacid on a suitable "carrier" that increases the porosity of the ion exchange bed. Particularly suitable carriers are fibrous substances, in particular asbestos, in one for filtering purposes suitable shape.

It has also been found that satisfactory and stable columns also have a physical Mixture of asbestos and the described salts of heteropoly acids can be obtained. the active particles adhere to the asbestos fibers. For example, the filling material for the columns can be prepared by weighing the desired amounts of active substance and carrier or gauges and slurries them with a dilute aqueous ammonium salt solution.

The best ratio of active substance to carrier will depend on the flow rate desired away. A ratio between 1:10 and 4: 1 is suitable.

The method of the present invention can also be applied to chemically analogous separations of non radioactive materials are applied.

The invention is to be explained in more detail below with the aid of examples.

Example 1 distribution coefficient

In order to illustrate the separability of ammonium phosphomolybdate and to compare it with the usual cation exchanger, the distribution coefficients Ka for the alkali ions in 1 molar ammonium nitrate solution were determined for both air-dried ammonium phosphomolybdate and for the strongly acidic ion exchanger with the protected trade name “Dowex 50” in the ammonium form. Balanced amounts of these exchangers were stirred overnight with a measured volume of the ammonium nitrate solution containing the radioactive alkali metal ion in question.

The Ka values, defined as

Quantity X per gram of exchanger ._ ,,., In equilibrium,

Quantity X per milliliter of solution

where X is the type of ion in question, were calculated from the decrease in the activity of the solution after equilibrium has been established.

From the following table it can be seen that the differences in the absorbability of ammonium phosphomolybdate are considerably larger than the "Dowex 50".

In addition, using the same conditions, the Ka values of thallium and silver were determined for ammonium phosphomolybdate only.

Furthermore, the Ka values of strontium and yttrium with ammonium phosphomolybdate were determined under the same experimental conditions, but keeping the pH constant at 2.7 and 3.5 using a sodium acetate buffer.

For some of the ions, the Ka values were determined in an analogous manner using ammonium arsenomolybdate (AAM), ammonium phosphotungstate (APW) and ammonium arseno tungstate.

Partition coefficient Ka, in 0.1 molar NH ₄ NO ₃

Cs Rb K N / A Tl Ag Sr Y Dowex 50 62 52 46 26th 5000 30th > 20 5300 APM 6000
4050 190 3 to 5 0 APW 202 AAW 4150 187 5.5 0 AAM

The total exchange capacities of these ammonium salts of heteropoly acids differ advantageous from those of conventional organic cation exchangers.

Example 2
Chromatographic separation of alkali metals

A small amount of ammonium phosphomolybdate was placed in a glass column 5 mm in diameter filled into a bed only 1.6 mm high. Two drops of one came into the top of the column Given a solution containing trace amounts of radioactive Na, K, Rb and Cs salts. Under use a column head 11 cm high, the elution with ammonium nitrate solutions was different Concentrations carried out. The initial flow rate was one drop per minute. Drops of the runoff were collected on plastic dishes, dried under an infrared lamp, and counted with a Geiger counter. Complete separation was achieved. Same partitions were achieved with an organic cation exchange resin, but were 250 times longer Columns required.

Example 3

Separation of Cs and Rb

1 g of ammonium phosphomolybdate was in an aqueous slurry with about the same Amount of weight of asbestos mixed and filled into a column up to a height of about 8 cm. That The total volume of the bed was approximately 14 ml. The ammonium phosphomolybdate was uniform in the bed distributed. 5 ml of a solution with a content of 10 mg each of Cs and Rb were in the upper Given to the end of the column and allowed to penetrate. The elution was carried out first with 4 molar, then with saturated ammonium nitrate solution (see FIG. 1), and in test tubes fractions of about 1 ml (15 drops) collected. These fractions were analyzed for radioactivity and the elution curve was applied. As shown in FIG. 1 shows a very satisfactory resolution achieved.

The flow rate was about 1 drop every 3 seconds. The maximum flow rate of the column with a liquid head of

However, ίο 5 cm was considerably higher, and the flow velocity therefore had to be regulated by using a rubber hose with a screw clamp. Hence there is no doubt that satisfactory flow rates can be achieved in this way and that the Process can be applied on an industrial scale.

Example 4
Flow rates

Ammonium phosphomolybdate and asbestos were weighed into beakers in the proportions given in the table below. Then 10 ml of a dilute NH ₄ NO ₃ solution were added, the constituents of the mixture were stirred and whisked together well and then transferred to the column. The same 0.9 cm diameter column with a glass wool stopper as a support, which was also the same for each batch, was used for each batch.

The ammonium phosphomolybdate mixture was allowed to settle and the liquid was allowed to drain off completely. Then the column was filled to its top with distilled water, and while the Flow rate (milliliters outflow per minute) was measured, the column was through continuous Adding water kept completely full.

Weight APM, g

Weight of asbestos, g

APM / asbestos weight ratio

Length of the column, cm

Flow rate, ml / min

In all cases the ammonium phosphomolybdate was evenly distributed in the beds.

Example 5

Separation of fission products
Ammonium phosphomolybdate

An 18 month old cleavage product solution was used for this experiment, which only included the following Fission products should be obtained in considerable quantities (the half-lives are given in brackets):

0.025
0.25
1: 10
3
3.9

0.025
0.25
1: 1
3
1.6

0.40
0.20
2: 1
2.1
0.7

0.60
0.15
4: 1
1.9
0.3

Sr (26 years)
Cs (33 years)
Ru (1 year)
Zr-Nb (65 days)
Tc (2 · 10 ⁵ years)
Sb (2.7 years)

Ce (280 days)
Pm (2.6 years)
(62 days)
(73 years)
(1.7 years)

Sm

Eu

Some of these elements produce short-lived fission products. The ones listed in the second column Elements are rare earths, with yttrium being a pseudo rare earth.

The activity of the pair Zr-Nb had probably largely disappeared due to the decay period, while technetium's contribution to total activity is believed to be due to its long half-life was very low.

A mixture of ammonium phosphomolybdate and asbestos in a weight ratio of 1: 1 was placed in a polyethylene column to form a bed of 0.61 cm ² x 5.0 cm. After the column was loaded successively with 0,0In- and ln-ammonium nitrate solution, the upper end of the bed were in the column 0.5 ml of a 2% strength sodium acetate buffer ^s (pH 4.5) and then immediately a drop of cleavage product solution containing of about 200 μ. per drop in dilute nitric acid and 0.5 ml of the buffer solution added. The solution was allowed to penetrate. Elution then took place as in FIG. 2 shown. Fractions of 5 drops each of the runoff were collected on aluminum plates, dried

and (about 10% activity) were counted with a Geiger counter, after each sample was left standing for about ¹ J ₂ hours after collecting the decay of short-lived separated Ba ^137th

As can be seen from the figure, a large part of the activity passed unadsorbed with the solvent front by.

It was found that the combined fractions 10, 11 and 12 contained Rh Ru 106 and Zr 95-Nb 95. The appearance of a small peak after the first peak was also found when the experiments were repeated and is also attributable to Ru 106.

The elution of the column with in-ammonium nitrate (pH 4.8) gave a very pronounced, mainly tip attributable to Sr 90.

When the column was further eluted with an acidic ammonium nitrate solution (In-NH ₄ NO ₃ + In-HNO ₃ ), another peak was obtained, which was much stronger than any previous one, which is attributable to the rare earths.

A subsequent examination of the column showed that more than 80% of the residual activity in the The upper half of the column were contained, while the lower tenth contained less than 1% of the total activity the column contained.

The y-spectra of the various sections showed that only a negligible amount of the activity in this lower section was attributable to ^{the Cs-137.}

In a second similar experiment, the highly retained cesium activity was saturated with Ammonium nitrate solution (see Example 3) eluted and appeared as a well-defined peak in the drain.

The same excellent separation results were obtained when the test with synthetic Mixing strontium, yttrium and cesium was carried out.

Example 6
Separation of Cd and In

There was an ammonium phosphomolybdate-asbestos column (weight ratio 1: 1) with dimensions of 1 cm x 4.0 ^a. Several times its volume of In-NH ₄ NO ₃ and then several times the volume of the column of 0, In-NH ₄ NO _{3 were allowed to} pass through the column. Then 6 ml of a solution of pH 4.0 containing 1.25 mg of Cd and 0.02 mg of In (each element made radioactive by irradiation in the atomic pile) was run through the column. 80 mg of sodium acetate were then passed through the column. First cadmium was eluted with n / 8-NH ₄ NO ₃ and then indium with In-NH ₄ NO ₃ + In-HNO _3. Fractions of 5 drops each of the runoff were collected and analyzed for radioactivity. The numerical values obtained were plotted in the same way as in the previous examples and gave two sharp and almost symmetrical peaks separated by almost 60 fractions with background activity.

Example 7

Separation of strontium and yttrium
Ammonium arsenomolybdate

This experiment was carried out in the same manner as that of the previous example. ^{A 2.9 cm x 1 cm 2} bed column was made with a packing material which also contained 0.9 g ammonium arsenomolybdate and 0.56 g asbestos; duration. The sample solution was prepared from 1 ml of a solution containing 1 mg each of Sr ⁹⁰ and Y ⁹⁰ and 4 ml of sodium acetate buffer. The flow rate was maintained at 3 drops per second.

After the sample was introduced and washed in the usual manner, the strontium was under

ίο Use of 3N ammonium nitrate as an eluent obtained as a well-defined, almost symmetrical tip with little attachment. The yttrium peak was obtained when eluting with In-ammonium nitrate + In-HNO ₃ as the eluent. The tips were completely separated.

: Examples

Extraction of Cesium 137 from an aqueous

solution

A very dilute solution of Cesium 137 was made slightly acidic and with an excess of Stirring ammonium phosphomolybdate. Some asbestos was added as a filter aid and the remaining solution first decanted and then filtered off. Through this treatment the Cesium became 137 practically quantitatively removed from the solution.

In the second attempt, the slurry was allowed to settle without the addition of a filter aid and only the residual solution was carefully decanted. The separation of the ^{ion exchanger loaded with Cs 137} from the residual solution could be accelerated and improved by centrifugation.

Claims (8)

Patent claims: 1. Process for the selective separation or enrichment of cations from acidic, aqueous Solutions by means of a solid inorganic cation exchanger and, if necessary, washing out of the exchanger, characterized in that ammonium phosphomolybdate, ammonium phosphotungstate, Ammonium arsenomolybdate or ammonium arsenotungstate, optionally on a support, is used, the selective ion exchange by adjusting the pH of the solution to be treated or the aqueous washing liquid is made possible. 2. The method according to claim 1, characterized in that the adjustment of the pH with a buffer substance. 3. The method according to claim 1 or 2, characterized in that one for selective exchange monovalent cations with a large ionic radius, especially cesium, from also polyvalent Solutions containing cations maintain a pH value below about 1. 4. The method according to claim 1 and 2, characterized in that to enable the exchange of bivalent and / or trivalent cations, in particular cations of elements of II. and III. Group of the periodic table of a possibly also containing monovalent cations Solution out moderately to weakly acidic conditions, in particular a pH of the solutions of 2 or above, preferably above 2.7. 609 507 / 234- ii 5. The method 'according to claim 1 to 4, characterized characterized in that the extracted ions are graded, preferably by fractional elution, be separated from the ion exchanger. 6. The method according to claim 5, characterized in -5 indicates that the eluent is an aqueous ammonium salt solution, optionally with an additive an acid * corresponding to the anion of the ammonium salt is used. ' 7. The method according to claim 1 to 6, characterized id characterized in that the ion exchanger in coarse, z. B. in granulated or tray tated form; - optionally with the addition of a binder, used, or the ion exchanger to increase the porosity with a Tiäger that preferably containing a fibrous substance is used. 8. The method according to claim 7, characterized in that that asbestos is used as a carrier, the ratio being exchangeable Substance to carrier is between 1: 10 and 4: 1. Publications drawn in consideration:
"Nature" (London), 1956 _? P. 1128/1129;
Vol. 181, 1958, pp. 1530/1531; Journal of the American Chemical Society, Volume 78, 1956, p. 694;
Industrial and Engineering Chemistry, 1955, p. 78. 1 sheet of drawings 609 507/3 + 2.66 © Bundesdruckerei Berlin